Bettas and ember tetras are temperature compatible but I wouldn't keep them together especially in such a small tank.
Platies have very little temperature overlap with bettas

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Honestly, since I live in Indonesia nobody in the fish market really cares about tempreture and because of that all the fish have adapted to the same tropical tempreture, because the fish market is somewhat outdoors with a roof.

What do you mean?
If the betta gets along with them for a few weeks or months it doesn't mean he will be fine with them forever. There have been so many stories of bettas living in a community tank for a while with everything going fine then finally one day it snaps. He may snap while you are not around and you come back to a tank of hurt/dead fish and one innocent looking betta. It may sound unlikely if you have been reading about people putting bettas in community tanks successfully because there are so many of these "success" stories but you hardly ever come across a betta in a community that has been working well for over a year where the tank is smaller than 30 gallons.
Bettas are not community fish. Even if they do not harm their tankmates he will be stressed with all the other fish on "his territory".
In a 10-12 gallon tank there is simply not enough room for fish to get away from eachother. In a 60 gallon tank with one betta and a school of 8-10 ember tetras it would probably be ok.

What do you mean?
If the betta gets along with them for a few weeks or months it doesn't mean he will be fine with them forever. There have been so many stories of bettas living in a community tank for a while with everything going fine then finally one day it snaps. He may snap while you are not around and you come back to a tank of hurt/dead fish and one innocent looking betta. It may sound unlikely if you have been reading about people putting bettas in community tanks successfully because there are so many of these "success" stories but you hardly ever come across a betta in a community that has been working well for over a year where the tank is smaller than 30 gallons.
Bettas are not community fish. Even if they do not harm their tankmates he will be stressed with all the other fish on "his territory".
In a 10-12 gallon tank there is simply not enough room for fish to get away from eachother. In a 60 gallon tank with one betta and a school of 8-10 ember tetras it would probably be ok.